The present invention relates to an anti-lock brake control method and system for motor vehicles.
In hydraulic brake systems for motor vehicles, there have been devised and demonstrated various anti-lock brake devices. For example, during the braking operation, when a brake pedal is depressed to cause the hydraulic pressure to be transmitted from a master cylinder to wheel cylinders, the rate of decrease in wheel speeds with respect to the vehicle speed or the drop in the wheel speeds with respect to the vehicle speed is detected, and the increase and decrease in the braking hydraulic pressure to be supplied to the wheel cylinders are alternately controlled in such a manner that the brake can be applied effectively without locking of the wheels, so that the driver can steer the motor vehicle in a desired direction. For instance, such anti-lock brake device is disclosed in Japanese Pat. Application Laid-Open Publication (Kokai) No. 60-61354 published April 9, 1985.
As described above, the conventional anti-lock brake devices employ a control system which repeats a control pattern that the wheel speeds with respect to the vehicle speed are decreased by increasing the hydraulic pressure transmitted to the wheel cylinders and then relieving the hydraulic pressure to wait for the recovery of the wheel speeds due to the reaction forces from the surface of the road, before increasing the hydraulic pressure again. Therefore, when the brakes are suddenly applied immediately after sudden steering in one direction (to be called "J-turn breaking" in general) so that the inner wheels rise up and the reaction forces from the surface of the road decreases as consequence, the braking force is adjusted to encounter such phenomenon to thereby prevent the wheels from locking. As a result, the braking force is unavoidably decreased. The above-described problem considerably adversely affects brake systems of the type wherein the hydraulic lines are arranged diagonally to cross each other and wherein the braking hydraulic pressures transmitted to the wheel cylinders of wheels are controlled in response to the lower wheel speed.